Controlling the hydrogenolysis of silica-supported tungsten pentamethyl leads to a class of highly electron deficient partially alkylated metal hydrides

N. Maity, S. Barman,E. Callens, M. K. Samantaray, E. Abou-Hamad, Y. Minenkov, V. D'Elia, A. S. Hoffman, C. M. Widdifield, L. Cavallo, B. C. Gates and Jean. Basset
Chem. Sci., 7, 1558-1568, (2016)

Controlling the hydrogenolysis of silica-supported tungsten pentamethyl leads to a class of highly electron deficient partially alkylated metal hydrides

Keywords

Tungsten pentamethyl

Abstract

The well-defined single-site silica-supported tungsten complex [([triple bond, length as m-dash]Si–O–)W(Me)5], 1, is an excellent precatalyst for alkane metathesis. The unique structure of 1 allows the synthesis of unprecedented tungsten hydrido methyl surface complexes via a controlled hydrogenolysis. Specifically, in the presence of molecular hydrogen, 1 is quickly transformed at −78 °C into a partially alkylated tungsten hydride, 4, as characterized by 1H solid-state NMR and IR spectroscopies. Species 4, upon warming to 150 °C, displays the highest catalytic activity for propane metathesis yet reported. DFT calculations using model systems support the formation of [([triple bond, length as m-dash]Si–O–)WH3(Me)2], as the predominant species at −78 °C following several elementary steps of hydrogen addition (by σ-bond metathesis or α-hydrogen transfer). Rearrangement of 4 occuring between −78 °C and room temperature leads to the formation of an unique methylidene tungsten hydride [([triple bond, length as m-dash]Si–O–)WH3([double bond, length as m-dash]CH2)], as determined by solid-state 1H and 13C NMR spectroscopies and supported by DFT. Thus for the first time, a coordination sphere that incorporates both carbene and hydride functionalities has been observed.

Code

DOI: 10.1039/C5SC03490F

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